Your default assumption should be that it's a scam; I've had two in the last year. Tell them that you've been scammed before (just to make them lick their lips) then ask for their name; ask for their number (not phone number, but shoulder tag number); ask what police station they operate from; ask for their rank, and which section they work in; then say "OMG, you must know old Frosty! How's the old b***r getting on?" If they threaten that they might send an officer around to interview you, say OK and ask when that might be convenient. Just when they are thinking they may have hooked you, tell them that in view of your previous scam you are nervous..... Hang up whenever you like during the previous routine.